HOW TO KNOW THE SEAWEEDS 



140b Lateral and terminal blades of similar shape and usually of simi- 

 lar size. Fig. 180 PterygophoTa calHornica 



Fig. 180. Pterygophora calif ornica Ruprecht 



An entire small intertidal plant, X 0.25. Occurs along the entire 

 Pacific Coast, mostly in infratidal beds where the plants reach a large 

 size of 8 feet or more in length. Intertidal specimens are smaller, more 

 scattered, and are absent in the southern part of the range although 

 the plant may commonly be found in driftweed. This species is a 

 perennial. Each winter the sporophylls, of which as many as 12 to 18 

 may mature in a season, disintegrate to leave scars on the stipe. 

 Some plants studied in northern Washington were estimated to be 

 thirteen years old from counts of the number of scars on the stipe. 



141a Thallus brownish; growth trichothallic. (This must be observed in 

 young, growing tips.) Fig. 181 Desmarestia (in part) 



Fig. 181. Desmarestia munda Setchell 

 & Gardner 



A small mid-portion of a plant show- 

 ing the very slender, opposite veins 

 and opposite branches characteristic 

 of the flat, ligulate members of this 

 genus, X 0.6. 



Several species occur more or less 

 widely along the Pacific Coast. The 

 only flattened Atlantic species, D. acu- 

 leata (Linnaeus) Lamouroux, is very 

 narrow and alternately branched, oc- 

 curring north of New Jersey. Cylin- 

 drical species of Desmarestia are treat- 

 ed under step 24a of this key. 



Figure 181 



Species of this genus are exceed- 

 ingly acid in character (pH 1.0) and 

 will damage other algae placed in 

 contact with them in field collections. 



139 



